The subject matter disclosed herein relates to the art of turbomachines and, more particularly, to a turbomachine compressor wheel member.
In conventional turbomachines, air is extracted from a compressor to cool hotter components such as, for example, turbine blades and nozzles. The air is generally extracted from a point as close as possible to an inlet of the compressor while still maintaining a sufficient backflow margin between source and sink pressure. As the axial position of the extraction is moved aft, turbomachine efficiency drops. That is, the further aft the extraction, the more work is put into the extraction air. As this work is not utilized, the overall efficiency of the turbomachine is lowered.
In certain cases, it is desirable to extract the air radially inwardly, toward a centerline of the rotor rather than radially outwardly thru the stator casing. When extracting air radially inward, the air must pass an inertia belt portion of the rotor. The inertia belt is an area of the cross-section of the rotor that impacts the ability to support sag due to gravity and internal axial stresses. In order to increase extraction airflow, the size of the extraction point must be enlarged. Enlarging the size of the extraction point requires the removal of additional material from the circumference of the rotor. This loss of material decreases the inertia belt, which, in turn, increases gravity sag and stresses. Towards that end, there is a limit to how much air can be extracted before the structural integrity of the rotor is compromised. One method for increasing the flow area is to have two or more arrays of axially spaced holes rather than one array of holes. However, this arrangement increases manufacturing costs of both the rotor and the stator.